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POTemplate class constructor overload resolution
 

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  1. POTemplate class constructor overload resolution
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    <p>I have a simple issue with ctor overload resolution for a class template:</p> <pre><code>#include &lt;iostream&gt; #include &lt;string&gt; using namespace std; enum EnumTypeVal { READ, WRITE }; template &lt;class T&gt; class TemplateClassTest { public: TemplateClassTest(const string &amp; stringVal, T typeVal, EnumTypeVal e = READ, const string &amp; defaultStringVal = "default"); TemplateClassTest(const string &amp; stringVal, const char * charVal); TemplateClassTest(const string &amp; stringVal, EnumTypeVal e = READ, const string &amp; defaultStringVal = "default"); private: T type; }; template &lt;class T&gt; TemplateClassTest&lt;T&gt;::TemplateClassTest(const string &amp; stringVal, T typeVal, EnumTypeVal e, const string &amp; defaultStringVal) { type = typeVal; cout &lt;&lt; "In TemplateClassTest(const string &amp;, T, EnumTypeVal, " "const string &amp;)" &lt;&lt; endl; } template &lt;class T&gt; TemplateClassTest&lt;T&gt;::TemplateClassTest(const string &amp; stringVal, const char * charVal) { cout &lt;&lt; "In TemplateClassTest(const string &amp;, const char *)" &lt;&lt; endl; } template &lt;class T&gt; TemplateClassTest&lt;T&gt;::TemplateClassTest(const string &amp; stringVal, EnumTypeVal e, const string &amp; defaultStringVal) { cout &lt;&lt; "In TemplateClassTest(const string &amp;, EnumTypeVal, const string &amp;)" &lt;&lt; endl; } typedef TemplateClassTest&lt;long long unsigned int&gt; u32Type; typedef TemplateClassTest&lt;bool&gt; boolType; int main() { u32Type l("test", "0"); //matches ctor 2 u32Type v("test", 0); // ambiguity between ctor 1 and 2 boolType b("test", "true"); //matches ctor 2 return 0; } </code></pre> <p>The second call fails to compile by throwing error:</p> <blockquote> <p>Call of overloaded 'TemplateClassTest(const char [5], int) is ambiguous.</p> </blockquote> <p>Why does <code>int</code> matches to <code>const char *</code>? This situation can be solved by changing the <code>const char *</code> to <code>const string &amp;</code> in ctor 2. But doing so, <code>boolType b("test", "true")</code> now gets matched to ctor 1 instead of ctor 2.</p> <p>My requirements are:</p> <ul> <li><code>u32Type v("test", 0)</code> should match ctor 1</li> <li><code>boolType b("test", "true")</code> should match ctor 2.</li> </ul> <p>Limitations are:</p> <ul> <li>ctor 1 and 3 signatures can't be changed</li> <li>user code calls in main() can't be changed.</li> </ul> <p>Any help is highly appreciated..Thanks!</p>
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    1. USCode Warrior
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    1. COjust leave the template constructor and specialize it for T=char const*
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      1. USbobah
    2. CO`typedef TemplateClassTest<int> u32Type;` would solve the problem, as ctor 1 becomes an Exact Match. I'm not sure if that wouldn't break something different, as `int` is not required to have exactly 32 bits.
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      1. USdyp
    3. COThis is the perfect example of why C++11 added the `nullptr` keyword.
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      1. USManu343726
 

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